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MMWR 44(31);577-579

Publication date: 08/11/1995

Table of Contents

Article

During July 12-16, 1995, Chicago experienced unusually high
maximum daily temperatures, ranging from 93 F to 104 F (33.9 C to
40.0 C). On July 13, the heat index* peaked at 119 F (48.3 C) -- a
record high for the city. This report describes the heat- related
deaths reported by the Cook County Medical Examiner's Office
(CCMEO) during this heat wave.

Deaths classified as heat-related by the CCMEO met one of the
following three criteria: 1) core body temperature of the decedent
greater than or equal to 105 F (greater than or equal to 40.6 C)
at the time of or immediately after death, 2) substantial
environmental or circumstantial evidence of heat as a contributor
to death (e.g., decedent found in a room without air conditioning,
all windows closed, and a high ambient temperature), or 3) decedent
in a decomposed condition without evidence of other cause of death
and with evidence that the decedent was last seen alive during the
heat wave period.

During July 11-27, a total of 465 deaths were certified as
heat-related by the CCMEO Figure 1; during July 4-10, no deaths
were certified as heat-related. The highest number of heat-related
deaths previously certified by the CCMEO -- associated with a heat
wave in 1988 -- was 77. The number of heat-related deaths peaked 2
days after the heat index peaked. Deaths increased from 49 (July
14) to a maximum of 162 (July 15) Figure 1. Of the 465 decedents,
257 (55%) were male. Based on race-specific data, 229 (49%)
decedents were black; 215 (46%), white; and 21 (5%), other
racial/ethnic groups.** Within racial categories, 128 (56%) blacks
were male, and 114 (53%) whites were male. Of the 437 decedents for
whom age could be determined, age ranged from 3 years to 103 years
(median: 75 years, mean: 72 years); 222 (51%) were aged greater
than or equal to 75 years.

During July 13-21 (when most heat-related deaths were
certified by the CCMEO), a total of 1177 deaths occurred in
Chicago -- an 85% increase over the same period in 1994 (637 deaths).
Reported by: ER Donoghue, MD, MB Kalelkar, MD, MA Boehmer, Office
of the Medical Examiner County of Cook, Chicago; J Wilhelm, MD, S
Whitman, PhD, G Good, MS, S Lyne, RSM, Commissioner, City of
Chicago Dept of Health; J Lumpkin, MD, L Landrum, MUPP, BJ Francis,
MD, State Epidemiologist, Illinois Dept of Public Health. Div of
Environmental Hazards and Health Effects, National Center for
Environmental Health, CDC.

Editorial Note

Editorial Note: Excess mortality from hyperthermia and
cardiovascular disease during heat waves has been well documented
(2,3). The findings in Chicago by the CCMEO that blacks, males, and
the elderly appear to be particularly susceptible to heat-related
death are similar to previous studies of heat waves. During public
health crises such as heat waves, state-specific mortality data are
often incomplete or unavailable; therefore, data from medical
examiners' (MEs') offices may be used to assess mortality during
such crises. Although ME-based surveillance for heat-related deaths
can prompt timely public health responses during heat waves, use of
ME data is limited because of selection bias. Individual MEs and
other persons who certify deaths (e.g., coroners and attending
physicians) use varying criteria to determine which deaths are
heat-related, largely because no standardized definition exists.
In the United States, lack of a uniform definition for
heat-related death results in substantial variation in the criteria
used to certify such deaths. The most stringent definition of
heat-related death is a core body temperature of greater than or
equal to 105 F (greater than or equal to 40.6 C) taken at the time
of death, with no other reasonable explanation of death. This
definition precludes certifying any death as heat-related if core
body temperature is not measured before or near the time of death
and may underestimate excess heat-related mortality. A nonspecific
definition of heat-related death (which could include all deaths
that occur during a heat wave) would overestimate this mortality.
The definition used by the CCMEO to classify deaths as heat-related
has remained unchanged since 1978 and is based on a reasonable
approach (i.e., evidence of exposure to high levels of
environmental heat). These two factors (as well as the finding that
the data about heat-related deaths are consistent with preliminary
data about total mortality in Chicago during July 1995) suggest
that the CCMEO data did not overestimate heat-related mortality
during that period.

The differential impact of a heat wave on specific population
subgroups cannot be determined based on ME data alone because of
incompleteness and potential bias (3,4). For example, based on
CCMEO data, a disproportionately high number of heat-related deaths
occurred among blacks in Chicago on July 15 Figure 1. Because
CCMEO data do not include all deaths nor equally represent all
socioeconomic status (SES) categories, it is not yet possible to
completely describe mortality, calculate death rates, or determine
whether the race- and sex-specific distribution of the heat-related
deaths is disproportionate to overall mortality in Chicago. A
case-control study is under way in Chicago to examine the
influences of SES and specific environmental factors on
heat-related mortality.

Despite their limitations, the data in this report confirm
that 1) public health information should be directed toward
susceptible populations (e.g., the elderly), 2) as in other heat
waves (2,3), the time between the beginning of a heat wave and the
resulting heat-related deaths (e.g., 2 days in Chicago) should be
sufficient to disseminate prevention messages to the public, and 3)
a standardized definition of heat-related death is needed.
Heat-related mortality is preventable. The most effective
measures for preventing heat-related illness and death include
reducing physical activity, drinking additional nonalcoholic
liquids, and increasing the amount of time spent in air-conditioned
environments. In addition, because increased air movement (e.g.,
fans) has been associated with heat stress when the ambient
temperature exceeds approximately 100 F (37.8 C) and because fans
are not protective at temperatures greater than 90 F (greater than
32.3 C) with humidity greater than 35% (the exact temperature
varies with the humidity), fans should not be used for preventing
heat-related illness in areas with high humidity (3,5). To further
define information that can be used to identify persons at greatest
risk during hot weather, CDC is collaborating with Chicago and
Illinois health officials to determine risk factors to better
target persons at increased risk for heat-related illness or death.
A standard definition for heat-related death will be addressed at
the February 1996 meeting of the American Academy of Forensic
Sciences.

Lee DH. Seventy-five years of searching for a heat index.
Environ Res 1980;22:331-56.

* The heat index (i.e., the apparent temperature) is an estimation
of the influence of temperature and humidity on the evaporative and
radiative transfer of heat between a typical human and the
atmosphere. The values can be derived from a chart available
through the National Weather Service (1).

** The CCMEO categorizes race of decedents as black, white, or
other.

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Figure 1

Number of heat-related deaths, by date of occurrence and race ..

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